1. Field of the Invention
This invention relates to a wireless data communication system and particularly to a wireless data communication system for communicating data within a limited space.
2. Description of the Prior Art
A wireless data communication system including at least a cell where a base station and a plurality of mobile units are provided is known. As a such wireless data communication system, a space transmission module is disclosed in Japanese patent application provisional publication No.62-233841. FIG. 13 is a block diagram of the prior art space transmission module. Numeral 13 is a coaxial cable, numeral 14 is a termination circuit, numeral 15 is a terminal equipment, numeral 16 is a satellite, and a numeral 17 is a terminal.
A signal from the terminal equipment is transmitted into the space by the terminal 17 comprising a photoelectric conversion element or an antenna. A satellite 16 receives the transmitted signal from the terminal 17 and converts it into an electric signal and supplies it to the coaxial cable 13 and detects a signal from the coaxial cable 13 and transmits the detected signal to the space. Then, the terminal 17 receives the signal from the satellite 16 and converts it by the photoelectric conversion element or the like and supplies it to the terminal equipment 15. The satellite 16 compares the signal supplied to the coaxial cable 13 with the signal from the coaxial cable 13 to detect a collision of the signal supplied to the coaxial cable 13 with signals from more than one other satellites 16 at the same time. If the satellite 16 detects the collision, it transmits a collision signal to the terminal 17. The terminal 17 receives the collision signal and informs of the collision to the terminal equipment 15. If the satellite 16 detects no collision, the satellite transmits the signal from the coaxial cable to the terminal 17. The terminal 17 further compares the received signal from the coaxial cable and the transmitted signal to detects a collision. As mentioned, in the prior art space transmission module, the terminal equipment 15 effects communication with the collision prevented.
However, in the above-mentioned carrier sensitive multiple access with collision detection (CSMA/CD) system, there is a problem that the carrier sensing cannot be effected due to a variation in the magnitude of the received signal by the multipath phasing by reflection and scattering in a room or a shadow phasing by the movement of a human body.